Ball bearing mounts to retain two devices in generally fixed position despite relative movement between the objects are well known. For instance, U.S. Pat. No. 4,593,957 by Hidano shows an arrangement of mating grooves on telescoped channel shaped members which hold ball bearings in machined grooves to provide a load bearing mount while accommodating rectilinear movement between a table and bed. In Hidano, a roller bearing is used for carriage mounting and accommodating relative movement. A rail of a C or U-shaped cross section carries within it two track grooves; similarly, a second channel shaped rail on the carriage carries V-shaped grooves within it. Ball bearings are positioned within the V-shaped grooves between the two channel shaped rails. In this arrangement, point contact is provided between the ball bearings and the V-shaped grooves so that, over a course of time, flats are worn into the ball bearings and into the grooves. As a result, both dimensional stability and parallelism are lost.
Another arrangement for guide wheels and tracks to allow relative motion between two members is shown in U.S. Pat. No. 3,661,431 by Wisecarver wherein bearing wheels have V-shaped circumferential grooves and sloped sides to mate both sides of an inverted V-shaped track, or to run on V-shaped tracks mating with the grooves. That is, Wisecarver relates to an angle track which makes contact with two grooved rollers, one on each side of the angle. The arrangement is obviously a problem in copier scanning mechanisms because of point contacts which wear between the mating surface of the rail and roller.
The aforementioned prior art does not suggest a single C-shaped rail with a tracking surface on the flat side and a grooved surface for controlling positioning on the underside, nor does this prior art relate to copiers and the problems associated with scanning carriages in related devices.
Contemporary dual carriage copier and scanner machines typically use shafts of a circular cross section with three or more ball bearings journaled around the shaft to make contact therewith. The result is a point contact at the three intersections of the shaft and the ball bearings. Over the course of time, both the shaft and the bearings form flat spots at the point of contact bringing about a change in the carriage position. Additionally, the machining operations of the shafts is such as to provide small grooves which are perpendicular to the scanning direction. Thus, as the bearings roll over the shaft, there is considerable noise particularly when the machine is new. Typically, in prior art copiers and scanners, both carriages ride on the same rail such that one carriage is nested within the other carriage.
None of the known prior art allows for precision mounting of a carriage so that wear is accommodated and predictable tracking of the carriage position is obtained. Further, none of the prior art carriage mounts for multiple carriage systems allow relative motion between the carriage beds with wear accommodation so that the carriage beds between two mounted carriages are moveable with precise location relative to one another, as is taught by this invention.